A sequence chart that shows an exemplary prior art of a network coding packet communication system in a wireless network is shown in FIG. 1.
In conventional systems to provide multicast communications, referring for example to FIG. 1, a first mobile terminal ST1 receives multicast data with a access point in the conventional packet communication method, and a second mobile terminal ST2 also receives the same multicast data access point. Accordingly, when the first mobile terminal ST1 transmits an uplink packet to the access point, the access point as well as the second mobile terminal ST2 suitably receives the uplink packet from the first mobile terminal ST1. Likewise, if the access point suitably transmits a downlink multicast packet to the first mobile terminal ST1, both the first mobile terminal ST1 and the second mobile terminal ST2 receives the downlink packet.
In reference to FIG. 1, if the first mobile terminal ST1 does not receive a downlink multicast packet (hereinafter, referred as to a first packet error) from the access point because of a temporary communication problem, the first mobile terminal ST1 transmits a first negative acknowledgement responsive to the first packet error. Preferably, the first negative acknowledgement means that the first mobile terminal ST1 does not receive the first packet normally. Further, the access point receives the first negative acknowledge message, transmitted from the first mobile terminal ST1, in response to the first packet error, and stores the first packet and its sequence number an additional memory device.
The first negative acknowledgement is also delivered to the second mobile terminal ST2. It is assumed that the second mobile terminal ST2 normally receives the first packet from the access point though the first mobile terminal ST1 does not receive the first packet because of a temporary communication problem.
A second packet as another downlink multicast packet from the access point is normally transmitted to the first and second mobile terminals ST1 and ST2.
Further, if the second mobile terminal ST2 does not receive another downlink multicast packet (hereinafter, referred as to a third packet) from the access point because of a temporary communication problem, the second mobile terminal ST2 suitably transmits a negative acknowledgement responsive to the third packet error. Preferably, the access point suitably receives the negative acknowledge message, transmitted from the second mobile terminal ST2, in response to the packet error of the third packet, and stores the third packet and its sequence number in an additional memory device.
Preferably, the negative acknowledgement suitably generated by the second mobile terminal ST2 is also delivered to the first mobile terminal ST1. It is assumed that the first mobile terminal ST1 normally receives the third packet from the access point though the second mobile terminal ST2 does not suitably receive the third packet because of a temporary communication problem.
Regarding of a fourth packet from the access point, the first mobile terminal ST1 suitably transmits a negative acknowledgement to the access point. In the case of a fifth packet from the access point, the second terminal ST2 suitably transmits a negative acknowledgement to the access point.
Referring to FIG. 1, the first and the second mobile terminals ST1 and ST2 normally receive a sixth packet and an eighth packet from the access point. However, in a seventh packet from the access point, the first and the second mobile terminals ST1 and ST2 independently transmit a negative acknowledgement to the access point. In the case of a ninth packet from the access point, the first mobile terminal ST1 does not receive normally and then does transmit a negative acknowledgement to the access point but the second mobile terminal ST2 receives normally.
At set-up time, i.e., after transmitting a first to a ninth packets and receiving a feedback in response to the first to the ninth packets, the access point makes a packet set for restoration based on the feedback such as plural negative acknowledgements and transmits the packet set to the first and second mobile terminals ST1 and ST2. Herein, the packet set for restoration enables the first and second mobile terminals ST1 and ST2 to restore a downlink packet in response to a negative acknowledgement. The packet set for restoration is provided in a first case that the first and second mobile terminals ST1 and ST2 independently transmits different negative acknowledgements in response to different downlink packets or in a second case that the first and second mobile terminals ST1 and ST2 independently transmits negative acknowledgements in response to the same downlink packets.
Referring to FIG. 1, the access point transmits a first restoration packet (1⊕3) to the first and second mobile terminal ST1 and ST2, based on the first negative acknowledgements independently generated responsive to the first and third packets. The first restoration packet (1⊕3) includes a result of logic XOR operation to the first and third packets. The first packet set is relevant to the first cast that the first and second mobile terminals ST1 and ST2 independently transmits different negative acknowledgements in response to different downlink packets. Responsive to the first restoration packet (1⊕3), the first mobile terminal ST1 performs a logic operation, e.g., ((1⊕3)⊕3), to the first restoration packet (1⊕3) and the third packet already received from the access point in order to restore the first packet not received normally from the access point. Meanwhile, the second mobile terminal ST2 performs a logic operation, e.g., ((1⊕3)⊕1), to the first restoration packet (1⊕3) and the first packet already received from the access point in order to restore the third packet not received normally from the access point.
Based on the second negative acknowledgements independently generated responsive to the fourth and fifth packets, the access point transmits a fourth restoration packet (4⊕5) to the first and second mobile terminal ST1 and ST2. The fourth restoration packet (4⊕5) includes a result of logic XOR operation to the fourth and fifth packets. The fourth packet set is also relevant to the first cast that the first and second mobile terminals ST1 and ST2 independently transmits different negative acknowledgements in response to different downlink packets. Responsive to the fourth restoration packet (4⊕5), the first mobile terminal ST1 performs a logic operation, e.g., ((4⊕5)⊕5), to the fourth restoration packet (4⊕5) and the fifth packet already received from the access point in order to restore the first packet not received normally from the access point. Meanwhile, the second mobile terminal ST2 performs a logic operation, e.g., ((4⊕5)⊕4), to the fourth restoration packet (4⊕5) and the fourth packet already received from the access point in order to restore the third packet not received normally from the access point.
In response to third negative acknowledgements from the first and second mobile terminals ST1 and ST2, the access point transmits a restoration packet, i.e., a seventh packet. In this case, the access point re-sends the seventh packet because both the first and second mobile terminals ST1 and ST2 do not receive the seventh packet normally. The first mobile terminal ST1 receives the seventh packet to recover the seventh packet not received normally before the set-up time. Receiving the restoration packet, the second mobile terminal ST2 also restores the seventh packet not received before the set-up time.
The access point transmits the ninth packet again to the first and second mobile terminals ST1 and ST2 because of the fourth negative acknowledgement delivered from the first mobile terminal ST1. This case is not included in the first or second case, but the fourth negative acknowledgement is a kind of remaining negative acknowledgement delivered before the set-up time. Accordingly, the access point re-sends the ninth packet for restoration. Then, the first mobile terminal ST1 receives the ninth packet to recover the ninth packet not received normally before the set-up time.
In the conventional code packet communication system, the access point receives a negative acknowledgement responsive to a multicast downlink packet and transmits a packet set to the first and second mobile terminals ST1 and ST2. Accordingly, the packet set enables both the first and second mobile terminals ST1 and ST2 to restore the multicast downlink packet. That is, the access point does not make a packet set separately used in the first and second mobile terminals ST1 and ST2 for a restoration process.
Preferably, the conventional packet communication system may simplify the restoration process because the access point suitably transmits a data for restoration to both the first and second mobile terminals ST1 and ST2 at a time.
However, in the conventional code packet communication system, the first and the second mobile terminals ST1 and ST2 individually transmit a negative acknowledgement to the access point every time a downlink multicast packet is not normally received. Accordingly, under a wireless network having high fraction lost, a negative acknowledgement often occurs so that obstacle or problem such as a collision between negative acknowledgements can be generated and a bandwidth in a wireless network may decrease. Further, the access point in the wireless network should store the negative acknowledgement delivered from mobile terminals so that an additional memory device is required.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.